Pattern controlled milling machine



May 7, 1940.

M. E. MARTELLOTTI PATTERN CONTROLLED MILLING MACHINE Filed Jan. 31. 1938 4 Sheets-Sheet 1 y 7, 1940- M. E. MARTELLOTTI 2,199,465

. PATTERN CONTROLLED MILLING MACHINE Filed Jan. 31, 1938 Sheets-Sheet 2 j l ll/UE INVENT OR. BY /%w/a f/Vqfli MW ATTORNEY.

May 7, 1940.

PATTERN CONTROLLED Filed Jan. :51, 1938' M. E. MARTELLOTTI MILLING MACHINE 4 Sheets-Sheet 3 M 5 /68 M7 /74 V .l l i I T Q INVENTOR.

ATTORNEY;

y 1940. M. E. MARTELLOTTI 2,199,465

PATTERN CONTROLLED MILLING MACHINE Filed Jan. :51, 19:58 4 Sheets-Sheet 4 ATTORNEY.

Patented May 7, 1940 UNITED STATES.

PATENT OFFICE PATTERN CONTROLLED MILLING MACHINE Application January 31, 1938, Serial No. 187,819

11 Claims.

This invention relates to machine tools and more particularly to a pattern controlled milling machine.

One of the objects of this invention is to provide a simple, inexpensive hydraulic control circuit by which a tracer may efficiently and automatically vary the path of movement between .a work piece and a cutter in accordance with a pattern. 4

Another object of this invention is to provide an improved hydraulic control circuit for the purpose described which has individual pumps for controlling the separate movements and which is so contrived that oscillatory effects are eliminated.

A further object of this invention is to provide a hydraulic control circuit for a pattern controlled machine tool which is simple to construct and operate and which is composed of a 2m relatively few number of parts.

Other objects and advantages of the present invention should be readily apparent by reference to the following specification considered in conjunction with the accompanying drawings illustrative of one embodiment thereof, but it will be understood that any modifications may be made in the specific structural details within the scope of the appended claims without departing from or exceeding the spirit of the invention.

Referring to the drawings in which like reference numerals indicate like or similar parts:

Figure l is a vertical section through a machine embodying the principles of this. invention.

Figure 2 is an elevation showing the cutter and work support units.

Figure 3 is a detail section on the line 33 of Figure 1.

Figure 4 is a detail view of the trip mechanism 40 on the pattern support.

Figure 5 is a section on the line 53 of Figure 4.

Figure 6 is a diagrammatic view of the hydraulic control circuit. 7

This invention may be applied to a machine, such as shown in Figures 1 and 2, having a base In from which uprise two columns II and I2.

The column ll, shown in Figure 1, has a tracerher is. This crank is connected by a link to the tracer support l3.

The crank I9 is keyed to the shaft 2! which is journaled in bearings 22 carried by the column. This shaft extends to column l2, as shown in 5 Figure 2, and is connected by a link 23 to a cutter support carrier 24, which is pivotally mounted at 25 on the front of the column l2. The carrier 24 has a cutter spindle 26 journaled therein, which is connected by a belt 21 to an electric 10 motor 28 mounted on theunder side of the carrier for movement therewith. A suitably shaped cutter 29 may be secured in the end of the cutter spindle for movement through an arcuate path similar to the path .of movement of the tracer. 15 Thus the piston Il may efiect oscillatory movement of both the tracer and cutter. I

The pattern carrier 30, Figure 1, is pivotally supported at 3| on the base Ill for movement toward and from the tracer I5. This movement is 20 effected by a hydraulic motor comprising a cylinder 32 having a contained piston 33 which is connected by a piston rod 34 to a crank 35. This crank is connected by a link 36 to the top of the tracer support 30. The crank 35 is keyed to a 25 shaft 31 which is journaled in the upper part of columns II and I2. The shaft 3l'is also connected by a crank 38 and a link 39 to the upper end of a work carrier 40, Figure 2, which is pivotally mounted at 4| on the base Ill. It will now be apparent that the piston 33 is adapted to swing the pattern and work carriers through an arcuate path toward and from the tracer and cutter respectively. By properly controlling the movement of pistons I1 and 33, relative movement between the tracer and the pattern, and between the cutter and work may be effected in two directions whereby an irregular contour on the pattern may be reproduced in the work. i

A hydraulic control circuit whereby the tracer 40 may accurately-control these movements is diagrammatically illustrated in Figure 6 of the drawings. I

The tracer support l3 contains the tracer controlled valve including a plunger which is made in two parts. One part 42,Figure 6, is provided with an annular groove 43 which is made of such width that when the valve is in a neutral position, the groove will partially uncover ports 44 and 45. Since these ports and the groove control the flow in the feed line, it is preferable that these ports each be halfway open, so that upon movement of the member 42 in either direction from its central position, one or the other of the u ports will be further closed to restrict the flow in the feed line.

With the part 42 positioned so that the groove 43 is central with respect to the ports 44 and 45, end face 46 of part 42 is finished to the proper dimension so that it will partially uncover port 41. The second part of the plunger comprises the spool 48, and this is spaced the required distance from the face 46 by an adjustable spacing member 49 so that the face 5801 the spool 48 will partially uncover the port 5|. The spacing member 49 may consist of a bolt threaded into the end of the member 42 and held in desired position by a lock nut 52. I

The tracer I5 has an integral ball shaped portion 53 by which it is supported in a socket 54 carried by the flexible diaphragm 55. The diaphragm is clamped between the end of the valve housing 56 and the abutting end of the closure plate 51 which is threaded onto the end of the housing. The tracer has a rounded end 58 which extends into a conical socket 59 formed in the end of the spool 48. A spring 68 is interposed between the end of the housing 56-and the member 42, for continuously holding the parts in endto-end contact, and thereby normally holding the tracer I5 in coaxial alignment with the valve parts. It will be apparent, however, that upon direct axial pressure being applied to the tracer I5, the diaphragm 55 will flex a predetermined amount and thereby cause shifting of the tracer valve parts against the compression of spring 68; or upon lateral pressure being applied to the tracer I5, the end 58 of the tracer will climb the side of the conical depression 59 and thereby cause axial movement of the tracer valve parts. It should also be noticed that when the tracer is free, the spring 68 will shift the parts a sumcient distance against the resistance of the diaphragm to close ports 45 and 41 and completely open ports 44 and 5|.

The port 5| is connected by channel 6|, ports I91 and I51 of valve 89, and channel 6| to a first pump 62, which has an intake 63 through which fluid is withdrawn from reservoir 64; and a relief valve 65 connected to channel 6| to limit the pressure therein. The channel 6| has a branch connection 66 connected to a resistance coil 61, the terminus 68 of which returns to reservoir. The tracer valve has an additional port 69, located midway betweenports 5| and 41, which serves as a reservoir connection, the port 69 being connected to reservoir through channel 18. It will now be seen that the pump 62 will be continuously delivering fluid into channel 6|, and the pressure will normally depend upon the resistance at port 5|, because of the high resistance of coil 61, but this coil will permit a certain amount of leakage to reservoir when the port 5| is completely closed, and will also serve as a dampener to vibration of the fluid during sudden changes in pressure. The pressure in this line is also transmitted through branch 1|, interconnected ports 12 and 13 of stop valve 14, channel 15, interconnected ports 16 and 11 of valve 18, and channel 19 to port 88 ofcylinder 32 and thereby to the large end of piston 33.

The port 41 of the tracer valve is connected by channel 8| to a second pump 82 which has an intake 83 througlr which fluid is withdrawn from reservoir 64; a relief valve 84 connected to channel 8|; and a high resistance leakage coil 85 which functions in the same manner as coil 61. The pressure established in line 8| by the resistance of port 41 is communicated through channel 86,

-valve 89. This porz control cam I I I.

interconnected ports 81 and 88 of. valve 89, channel 98, interconnected ports 9| and 92 of valve 18, and channel '93 to port 94 of cylinder 32 and thereby to the small end of piston 33. I

Since the piston 33 is a differential piston, it will be apparent that if the unit pressure established on one side of the piston is equal to the unit pressure established on the other side, that the total pressure in the large end will be greater than the total pressure in the small end, and the piston will move upward, as viewed in Figure 6. It is desirable, however, that when the tracer valve is in a central or neutral position with ports 45 and 44 open equal amounts, that no movement of piston 33 should take place and therefore the resistance at port 5| should be less than the resistance at port 41, assuming that the pumps 62 and 82 are of equal capacity and delivering the same amount of fluid into their respective delivery channels. Therefore the spacing member 49 is so adjusted that the port 5| is open a larger amount than the port 41 so that the resistance of port 5| ,will be less than the resistance of port 41, whereby a higher unit pressure will be established in line 8| than in line 6|. If the piston 33 has a 2-1 differential area, then the unit pressure in channel 8| should be twice that in channel 6|.

In this machine the cutting or feeding stroke corresponds to upward movement of the tracer and cutter, and therefore the connections are such that fluid pressure will be delivered to port 95 of cylinder I6 and thus to the small end of piston I1. This will cause rotation of the shaft 2| in such a direction that the cutter and tracer will move upward. Fuid for causing this feeding movement is supplied by a third pump 96, which has an intake 91 through which fluid is withdrawn from reservoir 64, and a delivery channel 91' which terminates at port 98 of valve 18. This channel also has a relief valve 99' connected thereto to limit the pressure "therein.

During a cutting stroke, the stop valve 18 is in such a position that the port 98 is interconnected by an annular groove 99 to port I88, which in turn is connected by a channel I8I to port I82 of is connected by annular groove I83 to port I8 which in turn is connected by channel I85 to ports I86 and I81 of a rate control valve I88. The valve I88 has a plunger I 89 which is normally urged in one direction by a spring ||8 against the periphery of a feed rate This cam is supported on a shaft 2 which may be rotated through suitable means to variably control the longitudinal position of plunger I89. This plunger'has a central spool I I3 terminating at opposite ends in tapered portions I I4 and 5 which form resistances to flow through ports I86 and I81.

The feed rate control valve I88 is primarily a flow dividing valve in which the quantity of fluid flowing through 'ports I86 and I81 can be varied by proportionately varying the resistances at these ports, but in order to maintain the division of flow, it is necessary to provide a balancing valve II6. This valve has a couple of ports 1 and 8 which are connected by channels I I9 and I28 respectively to. ports |2| and .I22'of the rate valve I88. The valve 6 has another pair of ports I23 and I24, the port I23 being connected to reservoir through channel 18, and the port I24 being connected by channel I25 to port 95 of the feed cylinder I6.

A plunger I26 is reciprocably mounted in the balancing valve and has a central spool I21 which is of sufllcient width to' partly close the ports I23 and I 24 when in a central position. This serves to form resistances at these ports which balance with the resistances at ports I06 and II to maintain equal pressures in channels H9 and I20 so that the division of flow is maintained. The annular grooves I28 and I29 formed in the plunger I26 are in constant communication with ports III and I I8, and each groove has a diametrical bore I30 which intersect axial bores I3 I and I32 terminating at opposite ends of the plunger. By means of these connections the pressure in channels H9 and I20 is communicated to the ends of the valve and thereby act on opposite ends of the plunger. It will now be apparent that if the pressure in either line is greater than that in the other line, that the plunger I26 will shift due to the unequal pressures on the ends thereof, and thus readjust the hydraulic resistances at I23v and I24 until equal pressures are again established in lines II 9 and I20. In this way a division of flow is established whereby part of the fluid delivered by pump 96 may be by-passed to reservoir and the remainder utilized for feeding purposes.

The other end of cylinder I6 is provided with a port I33 which is connected by channel I34 to port 45 of the tracer valve. Thus the feed line is connected to one end of cylinder I6, and the other end is connected to reservoir through ports 45 and 44. The result would be a substantially constant feeding movement of the tracer and cutter, but changes in the contour pf the pattern resulting in movement of the tracer will tend to close either port 44 or 45 depending upon the direction of movement of the valve member 42 thereby throttling the return flow from cylinder I6 and retarding the feed rate. Movement of the tracer will also inversely change the resistances at ports 41 and I thereby unbalancing the pressure on opposite ends of piston 33 whereby the work may be adjusted toward and from the cutter in accordancewith variations in the pattern.

At the end of the upward stroke of the cutter and tracer, a dog I35 carried by the tracer support as shown in Figure 1, rotates the lever I36 in a counterclockwise direction thereby pulling the rod I3! and rotating the crank I38. This crank is connected to the lower end of a shaft I39 which has a lever I40 keyed to it, Figure 3. This lever has a lost motion connection with a bell crank I4I which is supported for free rotationon the shaft I39. The lever I40 hasa pair of upstanding lugs I42 and I43. Upon rotation of the lever I40 in a counterclockwise direction, the lost motion between the lug I43 and the arm I44 of the bell crank I4I will be taken up during which time the spring pressed detent I45 will be riding to the peak I46 located between theindents I41 and I48 formed in the periphery of the lever I40. After the lever I40 has rotated a sufflcient amount for the detent lever to pass over the peak I46, the device will fire, and shift the valve plunger I49, to which the other arm of the bell crank MI is connected by pin I50, to a right hand position.

Referring to Figure 6, this will result in the closing of port I04 and the interconnection of port I02 to port I'5I. The feed pump 96 will now be connected through branch line I52 and line I34 to the right hand end of cylinder I6, tending to cause downward movement of the tracer and cutter. It will benoted that this is a direct connection by-passing the feed rate valve, whereby a rapid traverse movement can beeffected. The

lugs I68 and I69. connection with a valve shifter I which is supother end of cylinder I6 is connected, through a branch line I53 of line I25, to port I54, and

thus to port I55 and reservoir line I 56. Shifting of plunger I49 to the right closed port I9! and interconnected port I5.I with port 81, thus interconnecting two separate circuits. In other words, the delivery from pump 82 will flow throughchannel 86 and port .81 to port I51 and the combined flow from these two pumps will continue through channels 6| and II, interconnected ports I2 and I3 of stop valve I4, channel I5, interconnected ports I6 and II-of valve I8, and channel I9 to the lower end of cylinder 32 and effect a rapid traverse outward movement of the work and cutter supports.

The fluid from the other end of cylinder 32 will travel through channel 93, interconnected ports 92 and 9| of valve I8, channel 90 to port 88 of valve 89, the last named port now being connected to the reservoir port I58. The result will be that the work and pattern supports will start I to move away at a rapid traverse rate from the cutter and work supports; and the cutter and work supports will start to move downward at a rapid traverse rate. In order'to insure that no interference takes place during these rapid traverse movements between the pattern and tracer, the pattern support may be provided with a special block I59 which has an outwardly beveled surface I60 which projects beyond any part of the pattern so that the tracer will move upward on this surface a desired amount before the valve is tripped whereby, should the tracer startdownward slightly before the Work and pattern supports retract, no interferencewill t'ake place.

As the pattern carrier continues its outward movement, a dog I6I on the carrier hits a projecting lug I62 on a trip lever I63 thereby rotating the lever in a clockwise direction, as viewed in Figure 1. This lever is connected by a rod I64 to a crank I65 keyed to avertical shaft I66. As shown in Figure 3, the shaft I66 has a lever I6'I keyed thereto which carries a pair of upstanding This lever has a lost motion ported for free rotation on the shaft I 66. The valve shifter has a lug III which projects between the parts I69 and I68 whereby upon rotation of the lever I6'I, the lug I69 will take up the lost motion between it and the lug Ill, and while so doing, a detent lever H2 is riding up the inclined surface I I3 of indent II4 formed in the periphery of lever I6I. passes over the peak I15, it is spring pressed into the indent II6 whereby the parts are fired and the valve plunger III is shifted to the right.

Referring to Figure 6, this will effect interconnection of port I2 with port I18, and port I3 with port I19. This results in port I2, which is a pressure port and supplied from pump 62, being connected to reservoir through channel 90, interconnected ports 88 and I58, and channel I56. This cuts off the supply of fluid pressure from port 94 of cylinder 32. In addition, the interconnection of port I3 with port II9 resulted in the other port 80 of cylinder 32 being connected to the reservoir line I56. Since both ends of cylinder 32 are now connected to reservoir, further outward movement of the work and pattern supports will terminate.

In the meantime, the tracer and cutter supports were moving downward and this movement will continue until a dog I80 actuates the trip lever I 36, as shown in Figure 1, and shifts the valve plunger I49 of valve 89 to the left. This will When the detent I12 break the reservoir connection of port I18 of valve 14, by disconnecting port 08 from port I58 whereby the fluid pressure being supplied to port 12 will now continue through channels 90 and 93 to port 94 of cylinder 32 causing the work and blocked at port due to the tracer being unde-- fiected, no oil can escape from cylinder I6 and therefore no upward movement of the tracer and cutter will take place.

' As the pattern and work supports move inward,

the dog I6I will engage a second lug I8I on trip' lever I63, Figure 4, rotating the same in a counterclockwise direction and thereby shifting the valve plunger I11 back to the position in which it is shown in Figure 6. This will disconnect port 12 from channel 90 through the closing of port I18 so that the only fluid supply to channel 90 is from pump 82. Shifting of valve plunger I11 will also disconnect port 13 from port I19 and connect it to port 12 whereby the pump 68 is reconnected to port 80 of cylinder 32. Since the tracer is undeflected, port 5| ofv the tracer valve will still be open and therefore interconnected with the reservoir port 69 whereby pump 62, due to the interconnection of ports I51 and I91, will be discharging to reservoir and therefore unable to build up pressure in the large end of cylinder 32 whereby the piston 33 will continue its downward movement, as viewed in Figure 6, to bring the work and pattern into engagement with the cutter and tracer. The movement will continue until the pattern deflects the tracer and shifts the tracer valvea suflicient amount to increase the resistance at port 5I to the required degree that will raise the pressure in the large end of cylinder 32 equal to the pressure in the other end of the cylinder. Shifting of the tracer valve will also interconnect port 45 with port 44 whereby fluid can now escape from the large end of cylinder I6.

whereby the feeding movement will now start and the cycle willrepeat itself.

The machine may be stopped at any time by shifting the plunger of stop valve 18 to the left as viewed in Figure 6. The mechanism for shifting the valve comprises a hand lever I82 pivotally -mounted on an overhanging bracket I83 which projects from the column I I, as shown in Figure 1, and this lever is connected by a second lever I84 which is pivotally connected to a link I85. The link is pivotally connected through a crank I86 for rotation of a vertical shaft I81. This shaft, as shown in Figure 3, has a detent plate I88 integrally connected thereto, which has indents I89 and I90 formed in its periphery. A, spring pressed detent I9I is held in engagement with these indents.

The plate carries a pin I92 which has a lost motion connection with a notch I93 formed in the periphery of a shifter lever I94. This shifter lever is operatively connected to the valve plunger I95. When the shaft I01 is rotated in a counterclockwise direction, as viewed in Figure 3, the valve plunger I95 is shifted to the left, as viewed in Figure 6, thereby disconnecting the pump port 98 of the feed pump 96 from port I00 and interconnecting it to the reservoir port I96. This will terminate the feed movement. In addition, port 11 and 92 will be closed whereby. both ends of cylinder 32 are isolated from the rest of the circuit and the fluid in the cylinder will be impounded.

At the end of each cutting stroke it is desirable that the work and pattern supports be indexed, but since the indexing mechanism forms no part of the present invention, any suitable form of indexing means may be utilized, such as the indexing mechanism shown in the copending ap-- pllcation, Segal No. 138,639, filed April 23, 1937.

There has thus been provided a simple, inexpensive but highly efficient control circuit having separate pump circuits, one of which controls the feed movement, and two of which are connected to a motor for controlling the cross feed movement, means to vary the opposing pressures created by said pumps to vary the amount of said cross feed movement, and means to damp out oscillations caused by sudden changes in the opposing pressures.

What is claimed is:

1. In a pattern controlled machine tool having a relatively bi-directionally movable cutter support and work support, the combination of a piston operatively connected for effecting one direction of movement between the supports, a pair of pumps connected respectively to opposite ends of the piston, a tracer controlled valve, and means in the valve for variably impounding the fluid delivered by the pumps to difierentiate the resultant opposing pressures on the piston and thus determine the directions of said relative movement. 3 v

2. In a pattern controlled machine tool having a cutter support and a work support, the combination with means for efiecting a relative unidirectional feeding movement between the supports, ofa piston operatively connected for effecting a reversible movement between the supports angularly related to the direction of said feeding movement, fluid channels for supplying fluid pressure to opposite ends of said piston, a tracer controlled valve, separate means for supplying fluid pressure to said channels, means in the valve for controlling the pressure in each channel,- said valve having a central position for equalizing the resultant pressures on the piston to prevent movement, and other positions for differentiating the resultant pressures to efiect reversible movement in accordance with variations in a pattern. c

3. In a pattern controlled machine tool having a cutter support and a work support, the combination with means for effecting a relative feeding movement between the supports, of a hydraulic motor operatively connected for causing movement in an angular direction tothe feeding movement, a pair of pumps connected to said motor for effecting opposite directions of movement thereof, a tracer controlled valve, and means in the valve for variably impounding the fluid delivered by said pumps to equalize or difsaid supports, a relatively movable piston and cylinder, one of which is fixed and the other connected to one of said supports for'eflecting movement thereof toward and from the other support, a pair of pumps, separate channel means connecting the pumps to opposite ends of the cylinder, means in the tracer controlled valve for by-passing fluid from each of said channels to reservoir to variably control the pressure therein, said valve havinga first position for creating equal opposing pressures on said piston to prevent movement between the supports, and additional positions on either side thereof for inversely changing the opposing pressures on said piston for causing opposite directions of movement of the connected support.

5. In a contouring machine having a cutter support and a work support, the combination with a cooperating pattern and tracer jointly movable with the respective supports, of -means for producing an undulating cutting path in accordance with the contour of the pattern, including a first fluid operable means for efiecting one direction of movement, a second fluid operable means for eflfecting another direction of relative movement between said supports, embodying a fluid operable motor having a pair of ports,

independent means for supplying fluid pressure to said ports, and valve means controlled by the tracer for inversely impounding the fiuid delivered to said-ports for causing reversible operation 01' said motor.

6. In a machine tool, the combination with a tool support and work support, of means for eflecting relative movement between the supports, including a piston and cylinder, one of which is attached to the movable support and the other fixed with the machine, separate control circuits connected to the respective ends of the cylinder, each circuit including a pump, and ahydraulic resistance connection to reservoir, whereby the resistances may determine the total resultant pressures on opposite ends of the piston, and means to inversely change said hydraulic resistances to control movement of said piston. v

"I. In a machine tool, the combination with a tool support and a work support, of meansior efiecting relative movement between the supports, includinga piston and cylinder, one of which is attached to the movable support and the other fixed with the machine, separate hydraulic circuits connected to the respective ends or the cylinder, each circuit including a pump, and a hydraulic resistance connection to reservoir, whereby the resistances may determine the resultant opposing pressures on the piston. means to inversely change said hydraulic resistances to control movement of said piston. and means tointerconnect said circuits whereby the deliveryirom both pumps will flow to one end of the cylinder to effect a rapid traverse movement of the connected support.

8. In a machine tool having a cutter support and a work support, the combination of transmission means for efi'ecting'relative movement between the supports along two angularly related paths, including a first piston and cylinder, one of which is connected for eflecting movement along the first path; a second piston and cylinder, one of which is connected for effecting movement along a second path; a first pump: a

, one of two directions during uni-directional control circuit coupling the pump for actuation of the first piston in either of two directions; a second and third pump; separate hydraulic circuits connecting said pumps to opposite ends 01 the second cylinder; hydraulic resistance bypasses in each of said separate circuits for controlling the pressure of fluid therein and thereby the opposing resultant pressures on the second piston; and means to inversely vary said pressures whereby the second piston may be caused to remain stationary, or to be moved in either actuation of the first named piston.

9. In a profiling tool having a cutter support and a work support, the combination of hydraulic motors operatively connected to the respective supports for effecting movement thereof, means for supplying fluid under pressure to said motors, a tracer simultaneously movable with one of said supports for engagement with a pattern movable with the other of said supports, valve means controlled by the tracer for governing the distribution 01 fiuid to said motors whereby an undulatory cutting path between the cutter and work may be generated, and means trip operable by one of said supports for simultaneously reversing the direction of movement of each of said supports whereby the work will be separated from the cutter during rapid return movement of the supports.

10. In a pattern controlled machine tool having a cutter support and a work support, and hydraulic motors operatively connected to the respective supports for effecting relative movement therebetween in two directions, the combination with a tracer movable with one of said supports for engagement with a pattern movable with the other, of control means for said motors including a first pump for supplying fluid to one of said motors, a pair of pumps for supplying fiuid to the other motor, hydraulic resistances controlled by the tracer for controlling the discharge from said pair of pumps and thereby determining the opposing pressures on the connected motor and its direction of movement to effect approach and retraction movements between the work and cutter, and fixed hydraulic resistance leaks connected with each of said pair of pumps for damping oscillation in the respective pump circuits.

11. In a pattern controlled machine tool, the combination with a fluid operable slide for efiecting relative movement between a cutter and a work piece, of means for controllingsaid movement including a tracer controlled valve, a pair of pressural control channels terminating" in ports in said valve for governing movement of said slide, a first spool in said valve for determining the resistance at one of said ports and thereby the pressure in one of said channels, a second spool in said valve for determining the resistance at the other of saidports and thereby the pressure in the other of said channels, means for urging 'said spools toward one another, and

adJustable separating means between said spools whereby the resistance oflered by one of said.

spools may be independently adjusted with respect to the resistance offered by the other of said spools.

memo n. mammal-n. 7 

